Motorized lawn mowers of various types are well known for cutting grass or similar vegetation. These motorized lawn mowers generally include a housing having a cutting chamber, a rotatable cutting blade which is rotated in the cutting chamber and some type of motive means for effecting rotation of the cutting blade. Typical lawn mowers have been designed to incorporate one or more grass discharge ports where the cut grass is discharged by the operation of the cutting blade. The grass clippings are then deposited on the lawn and raking or gathering up the clippings is necessary when the grass is long. Alternatively, a bag attachment can be connected to the discharge port to collect the grass as it is discharged from the lawn mower.
As an alternative to clipping discharge and bagging chute type lawn mowers, numerous types of mulching lawn mowers are disclosed in the prior art that do not require bagging or raking of the grass clippings. These chuteless lawn mowers cut the grass clippings to a fine mulch which is deposited directly onto the lawn.
It is ecologically advantageous to deposit the mulched grass particles onto the lawn because they are a good nutrient source for the uncut grass. The grass particles decompose quickly and do not contribute to a build up of thatch as much as do longer length non-mulched clippings. Non-mulched clippings are often bagged and transported to landfills, contributing to the already significant solid waste disposal problems of landfills.
Prior art mulching mowers utilize various systems for initially cutting and recutting the grass clippings. Some systems utilize a toroidal chamber with a cutting blade that creates an air current for moving the cut grass clippings within the cutting chamber. The grass clippings are cut a plurality of times by the cutting blade before being deposited onto the grass. Other systems such as disclosed in U.S. Pat. No. 4,951,449 to Thorud utilize a plurality of planar members which are disposed along the inner wall of the cutting chamber. These planar members or "kickers" are utilized to deflect the grass clippings down into the direction and through the cutting plane. The blade subsequently directs the grass clippings onto the lawn. Still further, other systems utilize cutting elements with a plurality of cutting blades or members which increase the cutting action of the cutting element.
Regardless of the mulching system used in the prior art, it should be noted that the retention of grass clippings within the cutting chamber, and the requirement for these grass clippings to be cut a plurality of times in the mulching process, imposes a greater load on the motive source driving the blade than does a comparable non-mulching lawn mower. Thus, mulching lawn mowers utilizing electric motors as the prime motive source are subject to unique problems because they have comparably lesser horsepower outputs than mulching lawn mowers utilizing internal combustion engines.
Non-mulching chute type mowers generally have a tangential passage of air that exits the discharge chute located on the housing. In contrast, chuteless mulching mowers have less internal air current created inside the cutting chamber and are thus incapable of dissipating heat as easily as chute type non-mulching mowers.
Thus it becomes apparent that mulching mower designs that utilize electric motors as the prime motive source for rotating the cutting element must be concerned with special problems associated with electric motors. The overall drag that the cutting element produces in operation is of primary concern. Prior art mulching blade designs often include foil members or sail members that are utilized to create upward air currents within the cutting chambers of the mulching mowers. These air currents are utilized to disburse and circulate the grass clippings throughout the cutting chamber to facilitate movement of the clippings which must be recut a number of times before being deposited on the grass.
Conventional mulching blades are described in U.S. Pat. No. 3,085,386 issued to Slemmons and U.S. Pat. No. 4,189,903 to Jackson, et al. The utilization of large air foil or sail members on mulching mower blades requires increased horsepower to drive the blade as compared to regular lawn mower blades. The air resistance needed to create the air current for moving the clippings requires increased horsepower to rotate the blade.
An electric mulching mower is described in U.S. Pat. No. 4,318,268 issued to Szymanis. The Szymanis patent discloses a chuteless rotary mulching lawn mower powered by an electric motor including a toroidal cutting chamber bounded by a concentric skirt wall. The mulching mower blade disclosed in Szymanis includes an upwardly twisting portion for creating an upward air flow during rotation of the blade. The Szymanis mulching blade further includes a downwardly twisted portion for creating a downward air flow for pulling grass clippings down through the cutting plan and onto the grass.
The Szymanis application refers to electric mulching mowers utilizing electric motors. The Szymanis reference fails to address the significant obstacles posed in designing a battery powered electric mulching mower. Horsepower requirements of mulching mowers have in the past precluded implementation of battery powered mulching mowers because of the size and weight characteristics of the attendant battery power sources relative to the electrical energy requirements of mulching mowers. Battery sources possessing the electrical energy storage capacity large enough to supply continuous energy to an electric mulching mower during operation in mulching an average lawn size were often too large and too heavy for realistic consumer use.